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Mechanism of hyperosmolarity inhibition of vascular contractility
Insights
Hyperosmolarity inhibits vascular contraction by disrupting ion exchange. Restoring potassium and L-ascorbic acid partially reversed this effect for some vasoconstrictors, but not tyramine.
Area of Science:
- Physiology
- Vascular Biology
- Pharmacology
Background:
- Vascular smooth muscle contraction is regulated by various vasoconstrictor agents.
- Tissue osmolarity can influence vascular responses to these agents.
Purpose of the Study:
- To investigate the effect of hyperosmolarity on vasoconstrictor-induced contractions in the cat hind leg vasculature.
- To elucidate the underlying mechanisms of hyperosmolarity-induced inhibition.
Main Methods:
- Intraarterial infusions of vasoconstrictors (noradrenaline, angiotensin, tyramine, vasopressin) into cat hind legs.
- Induction of hyperosmolarity using hypertonic solutions.
- Perfusion at constant blood flow to isolate vascular effects.
Main Results:
- Hyperosmolarity significantly inhibited contractile responses to all tested vasoconstrictors.
- Inhibition was most pronounced with tyramine.
- Increased KCl or L-ascorbic acid partially restored contractility for noradrenaline and angiotensin, but not tyramine.
Conclusions:
- Hyperosmolarity-induced inhibition of vascular contraction is primarily linked to disrupted transmembrane Na+ and K+ exchange.
- Specific agents like tyramine may involve additional secondary mechanisms affected by hyperosmolarity.
Abstract:
Studies were made of the responses of the vascular bed of cat hind leg to intraarterial injection of noradrenaline, angiotensine, tyramine and vasopressine, as well as of carotid occlusion upon increasing the tissue osmolarity through intraarterial hypertonic infusion. The limb was perfused at constant blood flow. Hyperosmolarity inhibited the contractile effects of all stimuli studied. The inhibition of the contractility was greater in the case of tyramine and identical in the case of the remaining vasoconstrictor agents. Increased KCl content or the addition of L-ascorbic acid to the hypertonic solution with preservation of the same hyperosmolarity reduced the inhibition of the contractile responses to noradrenaline and angiotensine. The restoration of the contractility was much more pronounced upon simultaneous increase in the KCl content and addition of L-ascorbic acid. No recovery of the contractile effect of tyramine was observed. The mechanism of hyperosmolarity inhibition of the vascular contraction is discussed. In all vasoconstrictor stimuli the inhibition is connected primarily with disruption of the transmembrane exchange of Na+ and Ka+. In some vasoconstrictor agents, e. g. tyramine, there is disturbance in the specific mechanism connected secondarily with vascular contraction.